1. Field of the Invention
The present invention relates to an apparatus for vapor deposition and, more specifically to an apparatus for vapor deposition capable of forming a semiconductor layer and an insulating layer in a continuous manner with good productivity, which can be applied, for example, to a fabrication of EL devices.
2. Prior Arts
Thin film EL devices has been put into practical use with a so-called double insulating-layer construction such that a three-layer structure (insulating layer-EL layer-insulating layer) is sandwiched by a pair of electrodes at least one of which is transparent, because such a construction assures good stability and high reliability. In fabricating thin film EL devices of such a construction, it has been a conventional practice that a ZnS:Mn film is formed as an EL layer using an electron-beam evaporation technique while an Si.sub.3 N.sub.4 film or a like film is formed as an insulating layer using a reactive sputtering. In recent years studies are being conducted on a method for forming an EL layer using a Chemical Vapor Deposition technique (hereinafter abbreviated as "CVD") which can fabricate excellent EL devices (for example, Japanese Published Patent Application No. 47717/1985 and Japanese Unexamined Patent Application No. 296680/1986) and on a method for forming an insulating layer by CVD using an alkoxide (for example, Japanese Unexamined Patent Application No. 296680/1986 and J. A. Aborf: J. Electrochem. Soc. 114. 948, 1967).
In the case of fabricating thin film EL devices using any of the above methods, however, an insulating layer is first formed on a substrate with a first insulating layer-forming apparatus, then the substrate with the insulating layer is transferred to an EL layer-forming apparatus to form an EL layer, and thereafter the substrate with the insulating and EL layers is transferred back to the insulating layer-forming apparatus to form the second insulating layer.
Conventionally, as mentioned above, thin film EL devices have been fabricated by separately forming an insulating layer and an EL layer by means of different apparatuses, thus involving transfer of a substrate. This has resulted in a problem of low productivity in mass production of the EL devices.
Thus, the inventors of the invention have been trying to overcome the abovementioned problem and to provide an apparatus capable of continuously forming a semiconductor layer and an insulating layer in a shortened time and applicable to form the three-layer structure (insulating layer-EL layer-insulating layer) for EL devices.
As a result, the inventors of the present invention have formerly devised a CVD apparatus as shown in FIG. 3 and have examined the fabrication of thin film EL devices by the use of this apparatus (Japanese Unexamined Patent Application No. 289091/1989). The apparatus is so constructed that source materials are supplied from one end of a reactor 4 while exhausted from the other end thereof. Independent three heaters 7, 8a and 8b are provided around the reactor 4 for partly heating the reactor 4. The three heaters divide the inside area of the reactor 4 into three temperature regions, i.e., source material region A, temperature preadjusting region B and substrate temperature region C. A bubbling system 1 causes an alkoxide to be held by a carrier gas by bubbling, the carrier gas holding the alkoxide being introduced into the temperature preadjusting region B of the reactor 4 by means of a conduit tube 6. The alkoxide thus introduced is pyrolyzed and then deposited on a substrate 5 disposed in the substrate temperature region C to form an insulating layer. For forming an EL layer, a parent material and a luminescent center material are respectively placed within source supply tubes 2 and 3 disposed in the source material region A, and are led into the reactor 4 by means of a carrier gas. Thus, the EL layer is formed on the substrate 5. Thanks to the apparatus, the three-layer structure (insulating layer-EL layer-insulating layer) can be continuously formed in the single apparatus without transferring the substrate to another apparatus.
The above apparatus requires, however, a relatively long transition time for shifting from one layer to another. Referring to FIG. 4 which is a schematic temperature profile of the apparatus of FIG. 3. Although the substrate temperature is set to 400.degree.-600.degree. C. for forming any of the three layers, the source material region A and the temperature preadjusting region B are respectively maintained to 100.degree.-150.degree. C. and 200.degree.-250.degree. C. (see FIG. 4a) for forming the insulating layer because the alkoxide material starts pyrolyzing above about 300.degree. C. while set to 800.degree.-1000.degree. C. and 600.degree.-700.degree. C. (see FIG. 4b) respectively for forming the EL layer because a high temperature (800.degree.-1000.degree. C.) is required for sublimation of the parent material and for reaction of the luminescent center material with the carrier gas. Hence, respective temperatures of the source material region A and the temperature preadjusting region B need to be raised for forming the EL layer after the formation of the insulating layer while cooled for forming the other insulating layer after the formation of the EL layer. Consequently, it takes a relatively long time for forming the three-layer structure.